City attorney Grant Langley filed a request with the 4th District Court of Appeals on Wednesday to join a Madison teachers union and a Milwaukee city workers union as plaintiffs in the case.

Dane County Circuit Judge Juan Colas ruled in the unions' favor in September, but Republican Attorney General J.B. Van Hollen has filed an appeal.

Langley argued in his filing Walker's law violates the city's constitutional home rule powers because it prohibits the city from paying any portion of its employees' pension contributions. He also contended the law violates constitutional prohibitions on statutes impairing contracts.